New York Times: The Bush administration says the prospect of Iran's obtaining a nuclear weapon is "intolerable," and from the White House to the State Department, officials express considerable skepticism that Europe's efforts to negotiate quietly an end to Iran's nuclear activities will succeed. New York Times

By DAVID E. SANGER

This article was reported by Thom Shanker, Eric Schmitt and David E. Sanger, and was written by Mr. Sanger.

WASHINGTON - The Bush administration says the prospect of Iran's obtaining a nuclear weapon is "intolerable," and from the White House to the State Department, officials express considerable skepticism that Europe's efforts to negotiate quietly an end to Iran's nuclear activities will succeed.

Yet, though President Bush threatened Iraq before the war there, he has said almost nothing about the possibility of resorting to military action in Iran.

That may reflect the fact that Pentagon war planners, reviewing available options, say there are no good options for Mr. Bush - or for Israel, which has expressed even greater alarm about a nuclear-armed Iran if negotiations fail.

Almost unanimously, these planners and Pentagon analysts say there are no effective military ways to wipe out a nuclear program that has been well hidden and broadly dispersed across the country, including in crowded cities. Confronted with intelligence evidence, Iran admitted to inspectors last year that it had hidden critical aspects of its civilian program for 18 years, and even today there are questions about whether all of its nuclear-related sites are known.

The Bush administration has talked about the possibility of going to the United Nations to seek sanctions against Iran if a recent accord with the Europeans falls apart, as a similar agreement did last year. But the Iranians themselves are aware of the whispers about military strikes, many of them fueled by Israeli officials who view the threat as much more urgent than the Europeans do.

Even so, such talk may amount to little more than bluffing in a high-stakes diplomatic game that the deputy secretary of state, Richard L. Armitage, recently described as "kind of a good-cop, bad-cop arrangement," with Washington playing the bad cop. But a senior European official related a conversation in which Iranians deeply involved in the talks warned that any military action would be futile.

The official said the Iranians boasted that "they can rebuild the facilities in six months," using indigenous technology. He also said they believed that after any military action to slow Iran's program, they could "develop a weapon as a national cause, with more consensus than now."

Senior officers and Pentagon officials confirm that war planners, in particular Air Force targeting teams, have updated contingencies for dealing with Iran's nuclear ambitions, as they periodically do. But they immediately emphasize that this does not reflect any guidance from the civilian leadership to prepare for military confrontation.

Instead, they say, it is part of an effort ordered by Defense Secretary Donald H. Rumsfeld and Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, to begin a constant process of refreshing contingency planning throughout the world, an effort partly inspired by the outdated plan for invading Iraq that had to be rapidly dusted off and radically rewritten before the war there.

"Military planning always continues," said one senior officer based in the Middle East. "We are constantly updating plans."

But interviews with military planners, Pentagon policy makers and academic experts drew a unanimous sentiment that the challenge in 2005 would be to contain the situation so that neither the United States nor Iran took a misstep or miscalculated, bringing on military action.

The Iranians remember Osirak, the site of a lightning Israeli airstrike against an Iraqi nuclear reactor in 1981 that set back Saddam Hussein's nuclear ambitions by a decade. American and European intelligence officials say Iran has taken the lesson to heart, spreading its nuclear facilities around the country, burying some underground and putting others in the middle of crowded urban areas.

For example, the International Atomic Energy Agency last year found centrifuges, which are used to enrich uranium, behind a false wall at the Kalaye Electric Company in a densely populated corner of Tehran, where there would be no way to conduct a military strike without causing major civilian casualties. "They are not about to make the same mistake Saddam did," a senior administration official said.

Thus the military options range from the bad to the unimaginable.

None guarantee success, military planners say. Many risk causing not only casualties but a political crisis in the Middle East. The planners, many of them involved in the war against Iraq, argue vehemently that Iran presents a growing proliferation problem better approached through diplomatic channels than by airstrikes, Special Operations missions or an all-out invasion.

"There's no big war plan on the shelf," said one administration official involved in the planning process.

Part of the caution appears linked to the realization that while Iran's nuclear facilities are far more advanced than Iraq's ever were, the administration has yet to prove that Iran is secretly planning to build a weapon. The country has opened many of its sites to international inspectors, though there is still wrangling over whether the agency will be able to visit two military sites that some experts suspect could house a parallel, secret military effort to produce uranium.

If such sites exist, they would violate the nuclear nonproliferation treaty, which Iran has signed and which requires that all of its facilities must be solely for civilian use. So far, the inspectors have asked to see only one of the sites, and Iran has not indicated whether it would provide access.

The director general of the international agency, Mohamed ElBaradei, has carefully stopped short of declaring that Iran is seeking a weapon, though recently he noted that Iran "tried to cheat the system."

But whether it is a civilian program or something more nefarious, Iran is using an approach to developing nuclear fuel through the enrichment of uranium that is far easier to hide than the approach that Iraq took two decades ago.

So there is no central plant like Osirak to bomb.

"Osirak is not a paradigm," said Robert S. Litwak, director of international studies at the Woodrow Wilson Center here. "It was an exceptional case, in which all of the conditions for success came together. Israel had accurate intelligence on the target, collateral damage effects on the nearby population were judged minimal because the nuclear core had not yet been loaded into the reactor, and Saddam Hussein then had no capacity to retaliate directly against Israel."

In Iran today, said Mr. Litwak, who worked on proliferation issues as a National Security Council staff member in the Clinton administration, "none of those conditions pertain."

That view is echoed at the senior levels of the military. "Iran takes great care to protect its technology and production/storage capability with multiple layers of security, hardening and dispersal," said one Air Force general with experience in the Middle East. "All this complicates identification, targeting and execution."

Analysts of the Iranian political scene also point out that many in the American government view a growing and energized Iranian civil society, in particular the young and women, as an agent of change toward a democratic Iran.

News of the energy agency's restrained action helped Iran's stock market, which had suffered over fears that the nuclear dispute could result in a military confrontation with Israel or the United States. Any American military strike on Iran, these analysts say, would cancel any positive feelings these people have toward the United States, and probably galvanize support for the more militant Islamic leadership.